The present invention relates to expression of Mannose-Binding Protein (hereinafter xe2x80x9cMBPxe2x80x9d) in methylotrophic yeast strains.
Several MBP are described in U.S. Pat. No. 5,270,199. Each vertebrate is believed to possess its own form of MBP. MBP is thought to play a role in the disposal of pathogenic organisms. MBP works both by opsonisizing pathogen, and by activating the complement cascade. MBP consists of several monomers that assemble into one larger multimer. The multimeric form of MBP is believed to be necessary to activate the complement cascade.
Currently the only commercial source of MBP is from fractionated blood. Recombinant MBP has been produced by mammalian cell culture (Ezekowitz, U.S. Pat. No. 5,270,199), but yields are relatively low (20 to 40 mg/1) and attainable only at high cost due to the requirement for expensive culture media containing fetal calf serum. Thus, it has been desired in the art to produce MBP in high yields, and inexpensively, without the use of fetal calf serum.
Accordingly, an object of the present invention is to provide expression of multimeric MBP.
An additional object of the present invention to provide yeast strains that secrete high levels of MBP.
Another object of the present invention to genetically modify yeast strains to provide for increased multimerization of MBP.
These and other objects of the present invention, which will be apparent from the detailed description of the invention provided hereinafter, have been met in one embodiment by a methylotrophic yeast strain which encodes and expresses an MBP gene. Preferably, the yeast strain also encodes and expresses a protein disulfide isomerase (PDI) gene, prolyl-4-hydroxylase (P4H) gene, and heat shock protein 47 (hsp47) gene, and more preferably also the prolyl-4-hydroxylase (P4H) gene.